In refrigeration systems, the refrigerant, such as freon, frequently becomes contaminated with moisture, particles and acid and must be replaced. Until recently, it has been common for the old refrigerant to simply be vented into the atmosphere prior to the refrigeration system being recharged. It is now known that such vented refrigerant is harmful to the environment, particularly causing serious contamination to the upper atmosphere and destruction of the ozone layer. Recent legislation has restricted and prohibited such venting activities and requires the used refrigerant to be removed in a closed system and stored for later purification or disposal.
Several systems have been developed for removing and purifying the refrigerant for later usage. U.S. Pat. No. 4,805,416 discloses a system for recovery, purification and recharging of refrigerant in a refrigeration system in which a compressor is connected through solenoid valves to a combined heat-exchange/oil separator unit which condenses the refrigerant and separates the oil therefrom. After the refrigeration system has been fully evacuated, the refrigerant recovery system cycles the refrigerant by the continuous operation of vaporizing, drying and condensing until substantially all of the moisture has been removed.
A similar system is shown in U.S. Pat. No. 4,441,330 wherein refrigerant is evacuated from a refrigeration system through a particulate filter, evaporator, compressor and condenser to a storage container. Again, after evacuation, a multiple-cycle purification/drying process is carried out. Thereafter, oil is added back into the refrigerant which is used to recharge the refrigeration system.
In the aforementioned patents and other prior art, the refrigerant recovery unit is essentially taken out of further service when the storage tank has been filled until a purification cycle is completed. This purification process may require from two to eight hours, depending upon the nature of the filtering system. Thus, when a storage tank is full, the recovery unit cannot provide further recovery services until the refrigerant in the tank is purified. Alternately, if the filled tank is replaced by a new storage tank, the refrigerant in the filled tank must be purified later using another unit.
Another difficulty with prior art systems is that certain non-condensible gases have often contaminated the refrigerant and must be removed. For example, air commonly leaks into a refrigeration system and is drawn off when the refrigerant is evacuated. Since most of the air cannot be condensed in the recovery unit, there is a build-up of non-condensible gases in the storage tank with the liquified refrigerant which must be periodically purged to avoid intolerable high pressure.
Yet another problem in prior art recovery systems is the difficulty of venting the systems after the refrigerant has been evacuated. During evacuation, the compressor pumps the refrigerant from the refrigeration system leaving a near vacuum in the recovery unit line after evacuation. It is necessary to vent the line in some manner in order to change filters. However, in doing so, refrigerant may be vented to the atmosphere resulting in the detrimental effects discussed earlier.